This invention relates to displays and more particularly to a process of fabricating liquid crystal displays, capable of readily being automated, wherein continuous strips of plastic film are used, operated upon, and formed into liquid crystal display packages.
When properly aligned liquid crystal compositions are materials which exhibit reversible light modulation properties under an electric field. Normally the compositions are transparent to light, but in the presence of an electric field they scatter incident light. This characteristic has been extensively discussed in literature and will not be discussed in detail here. Further, exemplary liquid crystal compositions that are responsive to either D.C. or A.C. excitation voltages are well known.
Liquid crystal displays are known to operate in at least two basic modes, namely the reflective and transparent modes. The displays which are the subject of this invention are adaptable to either mode of operation. A reflective mode liquid crystal display device is comprised of a transparent electrode spaced from a second transparent electrode with the space between the two electrodes being filled by a liquid crystal composition. When an electrical bias is placed across these two electrodes the composition is subjected to an electric field which causes it to change its optical characteristics. This causes the contrast of the viewing plane formed by the reflective electrode to change in the region adjacent the portions of the liquid crystal composition which are subjected to the electric field. By shaping at least one of the electrodes to conform to the pattern or a portion of the pattern to be displayed a desired display pattern can be formed.
A transparent mode liquid crystal device consists of two transparent electrodes and a liquid crystal composition positioned therebetween. A light source is placed behind the liquid crystal display and selected regions of the composition are subjected to the influence of an electric field by applying an electric potential between the electrodes. The electric field causes the liquid crystal composition to scatter light. By shaping the least one of the electrodes to conform to a pattern or a portion of a pattern to be displayed the desired pattern can be formed.
Since, as described above the pattern displayed is determined by the shape of one or more electrodes, a liquid crystal display can be tailored to the desired application. Typical displays include the well-known seven segment display used for displaying digits between 0 and 9 as well as the dot display in which the pattern to be displayed is formed on a series of selectively placed dots. The dot type display may be formed by designing both the front and back electrodes of a liquid crystal display to have closely spaced electrically insulated conductors and orienting the front and back electrodes so that the respective conductors are orthogonal. The dot is formed by applying about one half the voltage required to cause the liquid crystal composition to scatter light to each of the electrodes. A dot is formed in region where the two electrodes cross.
Conventional liquid crystal display fabrication utilizes conductively coated and patterned glass. Between the two processed glass pieces a liquid crystal material is introduced, and a sealant is then introduced to enclose the liquid crystal between the processed glass pieces. The glass is processed by means of a photolithographic method to a conductively coated glass piece with selective etching of the conductor areas; applying an alignment layer; and orienting the alignment layer in the orientation necessary to effect a twisted nematic liquid crystal display. A second conductively coated piece of glass is similarly processed with a different electrode pattern and with an alignment layer oriented transverse to the direction of the alignment layer on the first glass piece. The first and second glass pieces are aligned and placed adjacent to and in contact with one another. The liquid crystal material is introduced between them, and a sealant is introduced between the glass pieces so as to trap the liquid crystal material in place. Finally, polarizers are aligned with and adhered to each of the first and second glass surfaces. The problems inherent in conventional liquid crystal display glass fabrication include incompatability with automated processing, necessitating human handling at critical stages of the process. Additionally, photolithographic etching limitations on resolution exists with larger displays on glass.